1,720,966 research outputs found
Choroid plexus trafficking of immune cells towards the rat cochlear nuclei after noise trauma or cochlear destruction
No full textCochlear nuclei are the first CNS station of auditory pathways, and the sole target of primary auditory fibers from the cochlea, which terminate in a frequency-dependent (tonotopic) pattern. Cochlear nuclei include a ventral nucleus (VCN) involved in binaural comparisons and a dorsal nucleus (DCN) involved in the integration of auditory and nonauditory stimuli. Circuital responses to peripheral damage, such as noise trauma or cochlear destruction, are quite different between VCN and DCN, possibly related to different auditory pathologies (e.g. tinnitus and speech comprehension deficit in noise vs errors in sound localization
in space). Microglial responses would be therefore expected to also display differences. However, most studies have so far concentrated on the VCN. We investigated the changes of DCN-related Iba1+ cells after 10 kHz noise trauma and unilateral cochlear destruction. A week after cochlear destruction, disorganized
clusters of Iba1+ cells appeared at the ipsilateral DCN surface facing the 4th ventricle, especially at contact sites with the choroid plexus and cerebellum, whereas a rod microglia train was observed at the surface of the contralateral DCN. An increase in ring-shaped and dystrophic microglia was also observed in the
ipsilateral DCN. In the choroid plexus, moreover, Iba1+ cells were significantly more numerous on both sides. Three days after noise trauma, Iba1+ cells increased in density and displayed activated morphology in the DCN region corresponding to noise trauma frequencies. At 12 days after trauma, activation had spread through the whole DCN, and superficial clusters of Iba1+ cells and choroid plexus Iba1+ cell increase was observed as for cochlear destruction. Morphological shifts were also observed in the microglial population, with an increase of ring-shaped and amoeboid (but not dystrophic) microglia. Minocycline bolished changes in Iba1+ cell density due to damage, although not morphological activation signs; stereotaxic (LPS) injections in the DCN induced instead a strong local amoeboid microgliosis. On the other hand, neither treatment affected choroid plexus macrophage density. These data suggest that the response of the Iba1+ population after peripheral trauma includes contribution from both local microglia and choroid plexus-derived factors. In order to differentiate Iba1+ populations and assess their relative importance, we labeled them selectively for CCR2 (for inflowing macrophages) and Tmem119 (for resident microglia). Moreover, we labeled other cell types (mast cells, neutrophils) at early stages after damage, counting them in choroid plexus and DCN parenchyma. The present work suggests that the DCN, in addition to integrating nonauditory context nerve signals with auditory stimuli, also integrates immune factors crossing its ventricular surface, possibly in order to differentiate physiological and pathological stimulation patterns
Trying hard not to listen: the evolution of information processing in vestibular hair cells
No full textVestibular afferents encode head movements with a discharge that
follows stimulus timecourse. In aquatic animals, both vestibular and
auditory stimuli are carried by water, and mainly differ in spectral power
content. For land animals, sounds are carried by air vibration that
minimally affect head movements, so that auditory and vestibular organs
receive separate inputs. It is therefore no surprise that auditory and
vestibular hair cells are much more similar in fish than in tetrapods. In
this work we compare the two different strategies for encoding vestibular
signals by hair cells in lower and higher vertebrates, and suggest a
possible pathway for the evolution of the vestibular organs (by modeling
the electrical membrane changes necessary and sufficient to transform
one encoding strategy into the other).
Amphibia represent a primitive transition to land life, and their inner ear is
primitive in many ways, containing organs, such as the saccule, which
cannot be classified as purely auditory nor vestibular. However, it also
displays proper vestibular organs, namely an utricle, a lagena and three
semicircular canals. For each vestibular organ, afferents display variations in
gain, dynamics, resting discharge frequency and regularity which are similar
to those in higher vertebrates, in particular a low-gain, phasic population is
observed, similar to fibers innervating type-I hair cells in amniotes. On the
other hand, hair cells still show primitive features, namely the presence, in
the population connecting to phasic fibers, of resonant behaviour due to a
Ca-BK system, which is absent in higher vertebrates, that instead possess
type I hair cells, which display a characteristic large M current which
profoundly change their electrophysiological properties.
We have investigated the membrane and release properties of frog
utricular and semicircular canal hair cells, by recording (with perforated
patch-clamp) current, voltage and release from hair cells differing in
morphology and epithelial position. Data from these experiments, together
with literature data for buffer expression and afferent innervation, and
immunohistochemistry data for intracellular Ca sources, were used to build
a NEURON model of utricular hair cells reproducing literature data for
afferent discharge. Our model show that Ca-BK resonance of phasic hair
cells, which is set at higher frequencies than vestibular stimuli, imparts a
phase advance to hair cell release relative to the mechanical stimulus, but
also introduces other linearity distortions, such as gain compression, which are not present in fibers connecting to type I hair cells. Assuming that during evolution from amphibia to reptiles no intermediate animal could survive without a working vestibular system, we explored (with NEURON models) possible transitions from a resonant, ICa-based cell to a nonresonant, IM-based cell that allowed phasic transduction in all intermediate stages
Hair cell-type dependent expression of basolateral ion channels shapes response dynamics in the frog utricle
No full textThe dynamics of vestibular afferent responses are thought to be strongly influenced by presynaptic properties. In this paper, by performing whole-cell perforated-patch experiments in the frog utricle, we characterized voltage-dependent currents and voltage responses to current steps and 0.3–100 Hz sinusoids. Current expression and voltage responses are strongly related to hair cell type. In particular, voltage responses of extrastriolar type eB (low pass, −3 dB corner at 52.5 ± 12.8 Hz) and striolar type F cells (resonant, tuned at 60 ± 46 Hz) agree with the dynamics (tonic and phasic, respectively) of the afferent fibers they contact. On the other hand, hair cell release (measured with single-sine membrane ΔCm measurements) was linearly related to Ca in both cell types, and therefore did not appear to contribute to dynamics differences. As a tool for quantifying the relative contribution of basolateral currents and other presynaptic factors to afferent dynamics, the recorded current, voltage and release data were used to build a NEURON model of the average extrastriolar type eB and striolar type F hair cell. The model contained all recorded conductances, a basic mechanosensitive hair bundle and a ribbon synapse sustained by stochastic voltage-dependent Ca channels, and could reproduce the recorded hair cell voltage responses. Simulated release obtained from eB-type and F-type models display significant differences in dynamics, supporting the idea that basolateral currents are able to contribute to afferent dynamics; however, release in type eB and F cell models does not reproduce tonic and phasic dynamics, mainly because of an excessive phase lag present in both cell types. This suggests the presence in vestibular hair cells of an additional, phase-advancing mechanism, in cascade with voltage modulation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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